Based on the analysis of the working principle of a twostage protection large flow safety valve, the mathematical model of the twostage protection safety valve was established; the hydraulic simulation models of the twostage protection large flow safety valve and the support including the safety valve were established by using the AMESim16.0 software, and the simulation analysis was conducted to obtain the cracking pressure and flow characteristic curve of the safety valve. In order to further explore the factors affecting the cracking pressure and flow characteristics of the twostage protection large flow safety valve, the diameter of the firststage directacting valve, the inlet diameter of the secondstage differential valve and the smallend diameter of the secondstage differential valve were changed, and the simulation analysis was carried out in the support hydraulic model.The results show that the cracking pressure is 40 MPa when the valve core diameter of the firststage directacting valve is 11.5 mm; the cracking pressure of the secondstage differential valve is 45 MPa when the inlet diameter is 34 mm and the small end diameter of the secondary differential valve is 30 mm. The simulation results provide reference for better application of the two-stage protection large flow safety valve.